Lanthanum is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals and is traditionally counted among the rare earth elements.
Protons and Neutrons in Lanthanum
Lanthanum is a chemical element with atomic number 57 which means there are 57 protons in its nucleus. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19 coulombs.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes. Isotopes are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes of Lanthanum are 139.
Main Isotopes of Lanthanum
Lanthanum occurs in 2 natural isotopes: 138La and 139La. 138La is very slightly radioactive, decaying by beta decay with a half-life of 1.05×1011 years. 139La is the most common isotope, having a natural abundance of approximately 99%.
Lanthanum-138 is composed of 57 protons, 81 neutrons, and 57 electrons.
Lanthanum-139 is composed of 57 protons, 82 neutrons, and 57 electrons.
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom of Lanthanum is 57. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration of Lanthanum is [Xe] 5d1 6s2.
Possible oxidation states are +3.
Most Common Application of Lanthanum
A lanthanum-nickel alloy is used to store hydrogen gas for use in hydrogen-powered vehicles. Lanthanum is also found in the anode of nickel metal hydride batteries (NiMH) used in hybrid cars. Lanthanum is an important component of mischmetal alloy. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15-18% neodymium with other rare earth metals following. The best-known use for this alloy is in ‘flints’ for cigarette lighters.
|Number of protons||57|
|Number of neutrons (typical isotopes)||139|
|Number of electrons||57|
|Electron configuration||[Xe] 5d1 6s2|
Properties of other elements